An olefin-metathesis reaction is a recombination reaction of intramolecular or intermolecular olefin double bonds of reactive molecules under a metal catalyst, and it has been confirmed that it is an essential and important reaction pathway for formation of carbon-carbon bonds in industries such as organic chemistry synthesis, polymers, and pharmaceuticals. Generally, transition metal catalysts utilized in the olefin-metathesis reaction comprise metal complexes of, for example, Ti, Ta, W, Mo, Ru or Os. Especially, a ruthenium complex containing a carbene ligand structure possesses superior catalytic activity, tolerance of functional groups and stability to air and water. Therefore, its development is fairly valued. Such catalysts were first developed by Grubbs and have been commercialized (trade names: for example, Grubbs I, II, III etc.). Other derivative structures of ruthenium complexes have also been developed for meeting the requirements of various olefin-metathesis reactions and are widely applied (trade names: for example, Hoveyda-Grubbs, Neolyst M1, Zhan 1B, nitro-Grela etc.).
Applying the olefin-metathesis reaction as a method for preparing low-molecular-weight nitrile butadiene rubber (NBR) is gradually becoming valued. Generally, hydrogenated nitrile butadiene rubber (HNBR) formed by hydrogenating nitrile butadiene rubber (NBR) is difficult to process further through a rapid injection molding process or a high-efficiency fluid injection molding process due to the doubling of its viscosity which deteriorates the processability of products, limiting its application in precise and complex devices. Viscosity of hydrogenated nitrile butadiene rubber is mainly influenced by its molecular weight. In order to improve the processability of hydrogenated nitrile butadiene rubber, reducing its viscosity is required, that is, appropriately controlling its molecular weight. Compared to conventional violent methods for treating nitrile butadiene rubber, for example mechanical grinding or chemical-acid decomposition, providing an olefin-metathesis catalyst with a specific catalytic activity to participate in the olefin-metathesis reaction of carbon-carbon double bonds in nitrile butadiene rubber molecules is capable of effectively degrading high molecular weight of nitrile butadiene rubber, avoiding deterioration. Also, the processability thereof is improved. Additionally, a narrow polydispersity index (PDI) of nitrile butadiene rubber is obtained, improving the physical properties of vulcanized rubber. The olefin-metathesis reaction of nitrile butadiene rubber is as follows.

In terms of existing technology, although a homogeneous-phase ruthenium catalyst system utilized in the olefin-metathesis reaction possesses high catalytic activity which is capable of effectively reducing the molecular weight of nitrile butadiene rubber, it is difficult to separate and recover such catalysts after reaction. On the other hand, such expensive catalysts often result in increased production costs. In order to overcome the potential problems of olefin-metathesis catalysts, the technology of loading a catalyst on a heterogeneous-phase carrier has been developed. A ruthenium catalyst with a designed ligand structure is fixed on a carrier to proceed to the olefin-metathesis reaction. In such a method, although the catalyst can be separated and recovered, the synthetic steps of the ligand structure are complex and the costs of raw materials are high, furthermore, the dispersibility and reactivity of the catalyst is pending further improvement. In regard to the nitrile butadiene rubber metathesis reaction system, it is difficult to separate and recover the nano carrier with high dispersibility due to high viscosity of reaction solution. Such problems can be improved by diluting the reaction solution. However, using large amounts of solvent is required, causing environmental pollution and increased treatment costs. Therefore, for relevant industries, the development of a low-cost catalyst system with high reactivity and capable of being easily separated and recovered to resolve the problems derived from applying the olefin-metathesis reaction to prepare low-molecular-weight nitrile butadiene rubber is desirable.